Method of forming a conductive contact

ABSTRACT

Conductive contacts in a semiconductor structure, and methods for forming the conductive components are provided. The method comprises depositing a conductive material over a substrate to fill a contact opening, removing excess material from the substrate leaving the contact within the opening, and then heating treating the contact at a high temperature, preferably with a rapid thermal anneal process, in a reactive gas to remove an undesirable component from the contact, for example, thermal annealing a TiCl 4 -based titanium nitride in ammonia to remove chlorine from the contact, which can be corrosive to an overlying aluminum interconnect at a high concentration. The contacts are useful for providing electrical connection to active components in integrated circuits such as memory devices. In an embodiment of the invention, the contacts comprise boron-doped and/or undoped TiCl 4 -based titanium nitride having a low concentration of chlorine. Boron-doped contacts further possess an increased level of adhesion to the insulative layer to eliminate peeling from the sidewalls of the contact opening and cracking of the insulative layer when formed to a thickness of greater than about 200 angstroms in a high-aspect-ratio opening.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. Ser. No. 09/941,533, filedAug. 29, 2001 (now U.S. Pat. No. 7,067,416).

FIELD OF THE INVENTION

The present invention relates to the field of semiconductor devicefabrication, and more particularly to methods for making conductivecontacts in the formation of a semiconductor device.

BACKGROUND OF THE INVENTION

As semiconductor fabrication moves toward maximizing circuit density,electrical components are formed at a number of layers and differentlocations. This requires electrical connection between metal layers orother conductive layers at different elevations in the substrate. Suchinterconnections are typically provided by forming a contact openingthrough insulating layer to the underlying conductive feature. Withincreasing circuit density, the dimensions of openings for electricalcontacts become narrower and deeper, posing a challenge to provideadequate conductive fill within high aspect ratio openings.

Typically, in forming a contact plug, a thin layer of titanium isdeposited over the top of a silicon base layer (substrate), and tungstenor other electrically conductive plug material is then deposited fromtungsten hexafluoride (WF₆) by chemical vapor deposition (CVD) to fillthe contact hole. However, there are several limitations of tungsten (W)plugs. Tungsten does not provide an adequate fill for high aspect ratiofeatures. In addition, the use of WF₆ as a precursor gas in theformation of tungsten plugs, can result in the penetration of thefluoride component into the adjacent dielectric layer causing lateralencroachment and wormholes.

Titanium nitride (TiN) films have attractive properties that mayovercome the limitations of tungsten plugs as integrated circuit (IC)devices continue to shrink below 0.15 micron dimension. TiN films havebeen deposited by low pressure chemical vapor deposition (LPCVD) usingtetrakisdimethyl-amidotitanium (TDMAT) and ammonia as precursor gases.However, TDMAT films have a high carbon content and when subjected tohigh temperatures in the presence of oxygen, become porous and,therefore, are unusable as a conductive contact.

Thin TiN films and liners have also been deposited from titaniumtetrachloride (TiCl₄) and ammonia (NH₃) by CVD onto a titanium (Ti)liner overlying the insulative layer. Although useful for forming a thinliner, when pure TiCl₄-based TiN is deposited to fill a via or othercontact opening, the material does not adhere well to the Ti thin layer,particularly when the TiN layer becomes greater than about 150 to about200 angstroms thick.

In addition, it has been found that chlorine (Cl₂) within a contact fillmaterial such as TiN, which has been deposited from achlorine-containing precursor such as TiCl₄, can diffuse into andcorrode an overlying interconnect (e.g., aluminum), thus ruining thedevice.

Another problem lies in the formation of a conductive contact (e.g.,contact plug) in a contact hole or via. Typically, a conductive materialis blanket deposited over the surface of the substrate including intothe contact hole, thus forming a continuous film. If an anneal isneeded, the continuous film layer is typically subjected to a hightemperature anneal, and then excess material is removed from the surfaceof the substrate by a chemical mechanical polishing (CMP) process,leaving the contact plug within the hole. A problem arises, however,during the high temperature anneal with cracking of the blanket materiallayer.

Therefore, it would be desirable to provide a conductive contact and amethod of forming the contact that avoids such problems.

SUMMARY OF THE INVENTION

The present invention provides methods for forming conductive contactsin the construction of semiconductive devices, and the conductivecomponents formed by those methods. The method is useful for fabricatingcontacts to electrical components beneath an insulation layer in anintegrated circuit such as memory devices.

The present TiCl₄-based titanium nitride films are particularly usefulas conductive contacts to replace tungsten (W) plugs in high aspectratio features, particularly openings and other features having anaspect ratio of 3:1 or greater. The films also overcome inadequacies ofpure TiCl₄-based titanium nitride films that are used as fill materialfor forming conductive contacts or interconnects within contact openingsformed through an insulative layer of a semiconductor structure. PureTiCl₄-based titanium nitride fills do not adhere well to the surface ofinsulative sidewalls of a contact opening, and can also cause theinsulative layer to crack due, at least in part, to the pressure exertedwhen the thickness of the fill within the contact opening is about 200angstroms or greater.

The present invention overcomes the problems of a pure TiCl₄-basedtitanium nitride plugs or barrier film by incorporating diborane (B₂H₆)into the gas mixture to dope the TiCl₄-based titanium nitride filmduring the deposition process. The addition of B₂H₆ to the precursor gasused to form the TiCl₄-based titanium nitride film has been found toimprove the mechanical properties of the resulting titanium nitride filmwith substantially no impact on its conductive properties. Inparticular, the gaseous mixture used to form the boron-doped, titaniumnitride contacts comprises diborane (B₂H₆) in an amount effective toprovide a contact having an amount of boron to provide a level ofadhesion of the conductive contact to the insulative sidewalls of thecontact opening to substantially eliminate peeling of the contact fromthe sidewalls and cracking of the body of the insulative layer. Themixture further includes an amount of ammonia (NH₃) to provide thecontact with a level of nitrogen effective to maintain the conductivityof the contact at a predetermined level for an effective electricalcontact with a conductive or active area within the substrate to/from anactive area within a semiconductor device and/or a memory or logicarray.

However, one drawback of titanium nitride films formed from TiCl₄,including the boron-doped films described herein, is that the chlorine(Cl₂) within the formed contact can diffuse into an overlying material,for example, an overlying interconnect of aluminum, and corrode and ruinthe device. It has been found that a high temperature anneal of theTiCl₄-based titanium nitride film in a nitrogen-containing atmosphere,preferably ammonia (NH₃), removes excess Cl₂ from the contact materialto overcome the diffusion problem. It has also been found thatconducting a CMP process to remove excess material from the substrateprior to the anneal step avoids undesirable problems with cracking ofthe film layer and the wafer substrate.

In one aspect, the invention provides methods for forming a contact in avia or other contact opening of a semiconductor structure. The openingis formed through an insulative layer to a conductive or active area,such as a source/drain region, in an underlying silicon substrate. Themethod is particularly useful for forming contacts within vias and otheropenings having an aspect ratio of about 3:1 or greater, and a widthdimension of about 0.25 μm or less.

According to an embodiment of the method of the invention, a conductivematerial is blanket deposited over the substrate to fill the opening,and excess material is removed from the surface, preferably bychemical-mechanical polishing (CMP), with the conductive materialremaining in the opening to form the contact. The contact is then heatedto a high temperature, preferably by use of a rapid thermal annealprocess, in a reactive gas to remove an undesirable component from thecontact material.

In an example of this embodiment of the method, a titanium nitridecontact can be formed by first depositing a seed layer comprisingtitanium silicide (TiSi_(x)) over the silicon substrate at the bottom ofthe contact opening, preferably to a thickness of about 250 to about 300angstroms, for example, from a plasma source gas comprising titaniumtetrachloride (TiCl₄) and hydrogen (H₂) by plasma-enhanced chemicalvapor deposition (PECVD). A titanium nitride or boron-doped titaniumnitride film (i.e., titanium boronitride, TiB_(x)N_(y)) can then bedeposited onto the seed layer to fill the contact opening, typically toa thickness of about 1000 to about 3000 angstroms. The film layer can bedeposited from a source gas mixture of TiCl₄, NH₃, and one or morecarrier gases, with the addition of B₂H₆ to form the boron-doped layer,by thermal CVD at a pressure of about 1 to about 15 Torr and atemperature of about 550 to about 700° C. The substrate is thenprocessed, preferably by CMP, to remove excess material from thesubstrate while leaving the titanium nitride material in the contactopening. The contact is then subjected to a high temperature in anitrogen-containing gas, preferably ammonia (NH₃) at above 700° C. witha rapid thermal anneal, to remove a high percentage of the chlorine(Cl₂) content from the contact material, preferably up to about 99% bywt.

In another example of the method of the invention, a multi-layeredtitanium nitride contact is formed within a contact opening of asemiconductive structure. A titanium silicide seed layer is first formedover the silicon substrate at the bottom of the contact opening. To formthe layered contact, alternating layers of titanium nitride andboron-doped titanium nitride can then be deposited over the seed layer.In forming the alternating layers, a layer comprising titanium nitride(undoped) can be deposited from a first gaseous mixture comprising TiCl₄and NH₃, to form a layer typically about 100 to about 500 angstromsthick. Diborane (B₂H₆) can then be introduced into the gaseous mixtureto deposit an intermediate layer of boron-doped titanium nitride to forma layer typically about 100 to about 500 angstroms thick. The flow ofdiborane into the gas mixture can then be stopped to deposit a nextlayer of titanium nitride layer that is not doped to a typical thicknessof about 100 to about 500 angstroms. Additional alternating layers ofdoped and undoped titanium nitride can be deposited to fill the opening,with the uppermost layer being undoped titanium nitride. Excess materialis then removed from the substrate by CMP, and the contact is subjectedto a heat treatment, preferably by a rapid thermal anneal, preferably inammonia at greater than 700° C., to decrease the chlorine (Cl₂) contentof the contact.

Another aspect of the invention is a conductive contact formed in asemiconductor structure of a semiconductor circuit. The semiconductorstructure comprises a silicon substrate, an overlying insulative layer,a contact opening formed through the insulative layer to expose theunderlying silicon substrate, and the conductive contact formed withinthe opening.

In one embodiment of a contact according to the invention, the contactcomprises a thermally annealed layer of titanium nitride and/orboron-doped titanium nitride overlying a titanium silicide layer formedover the substrate at the bottom of the opening, the contact having alow chlorine (Cl₂) content, preferably less than about 1% by wt.

In another embodiment, the conductive contact comprises multiple layersof thermally annealed titanium nitride overlying a titanium silicidelayer deposited onto the silicon substrate at the bottom of the contactopening, the contact having a low chlorine (Cl₂) content, preferablyless than about 1% by wt. The contact comprises alternating, overlyinglayers of undoped and boron-doped titanium nitride that fill the contactopening. An undoped titanium nitride layer overlies the titaniumsilicide layer, and also forms the uppermost layer of the conductivecontact. The thickness of each of the individual layers is typicallyabout 100 to about 500 angstroms.

Another aspect of the invention is an integrated circuit (IC) devicethat includes the foregoing conductive contacts comprising titaniumnitride and/or boron-doped titanium nitride. The IC device comprises anarray of memory or logic cells, internal circuitry, and at least onegenerally vertical conductive contact coupled to the cell array andinternal circuitry.

In one embodiment of an integrated circuit device according to theinvention, the IC device comprises a conductive contact comprising athermally annealed titanium nitride and/or boron-doped titanium nitridefill that is formed within an insulative contact opening over a thinlayer of titanium silicide deposited onto the exposed substrate at thebottom of a contact opening, and has a low chlorine (Cl₂) content,preferably less than about 1% by wt. In another embodiment of anintegrated circuit device, the conductive contact comprises thermallyannealed material having a reduced chlorine (Cl₂) content, preferablyless than about 1% by wt., that is multi-layered, comprising alternatinglayers of titanium nitride (undoped) and boron-doped titanium nitridedeposited onto a titanium silicide layer overlying the substrate at thebottom of a contact opening. The contact is in electrical contact withan active area such as a source/drain region of a transistor or a memoryor logic cell array, or other semiconductor device.

Advantageously, the present film overcomes limitations of tungsten plugfills in high aspect ratio devices, with parametric data showingsuperior results compared to that of tungsten. The films also have adecreased level of undesirably components such as chlorine that becomeincorporated into the film upon deposition of precursor gases to formthe film. The present method provides a process of removing undesirablecomponents such as chlorine and the like, from a contact which overcomesproblems in the art with cracking from anneal processing steps, andwithout adversely effecting other structures and devices formed on thesubstrate. The present invention provides processes for formingconductive contacts that are fast, simple and inexpensive to implementin semiconductor manufacturing.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below withreference to the following accompanying drawings, which are forillustrative purposes only. Throughout the following views, thereference numerals will be used in the drawings, and the same referencenumerals will be used throughout the several views and in thedescription to indicate the same or like parts.

FIG. 1A is a diagrammatic cross-sectional view of a semiconductor waferfragment at a preliminary step of a processing sequence.

FIGS. 1B through 1D are views of the wafer fragment of FIG. 1A atsubsequent and sequential processing steps, showing fabrication of aconductive contact according to an embodiment of the method of theinvention.

FIGS. 2A through 2F are views of the wafer fragment of FIG. 1A atsubsequent and sequential processing steps, showing fabrication of aconductive contact according to another embodiment of the method of theinvention.

FIGS. 3A and 3B are graphical depictions showing the amount of thermalstress (Gdynes/cm²) versus diborane (B₂H₆) flow over a range of 200 to600 sccm at reactor temperatures of 600° C. and 650° C.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention encompasses methods of making integrated circuits,particularly methods for forming conductive contacts for providingelectrical connection between conductive or active areas of discretesemiconductor devices or portions of such devices. In particular, theinvention relates to methods of forming a conductive contact having areduced concentration of unwanted constituents such as chlorine thatbecome incorporated into the contact, for example, from precursors,during formation. The invention further relates to a contact structureincorporating a titanium nitride and/or a boron-doped titanium nitridefilm having a low chlorine content. The present invention isparticularly useful in providing a conductive contact in openings andother features having a high aspect ratio of 3:1 or greater.

The invention will be described generally with reference to the drawingsfor the purpose of illustrating the present preferred embodiments onlyand not for purposes of limiting the same. The figures illustrateprocessing steps for use in the fabrication of semiconductor devices inaccordance with the present invention. It should be readily apparentthat the processing steps are only a portion of the entire fabricationprocess.

Integrated circuits include a large number of electronic semiconductordevices that are formed on varying levels of a semiconductor substrate.Exemplary semiconductor devices include capacitors, resistors,transistors, diodes, and the like. In manufacturing an integratedcircuit, the discrete semiconductor devices that are located onnonadjacent structural levels are electrically connected, for examplewith an interconnect or conductive contact structure. The conductivecontact generally comprises a region of conducting material that isformed between the semiconductor devices or portions of thesemiconductor devices that are being placed in electrical communication.The conductive contact serves as a conduit for delivering electricalcurrent between the semiconductor devices. Specific types of conductivecontact structures include local interconnects, contacts, buriedcontacts, vias, plugs, and filled trenches. The present inventionparticularly deals with the method of making conductive contacts thatare used in the fabrication of semiconductor devices.

In the current application, the terms “semiconductive wafer fragment” or“wafer fragment” or “wafer” will be understood to mean any constructioncomprising semiconductor material, including but not limited to bulksemiconductive materials such as a semiconductor wafer (either alone orin assemblies comprising other materials thereon), and semiconductivematerial layers (either alone or in assemblies comprising othermaterials). The term “substrate” refers to any supporting structureincluding, but not limited to, the semiconductive wafer fragments orwafers described above. The term “undesirable component” refers to anyelement or compound contained within the contact material that willadversely affect a semiconductor device, for example, a highconcentration of chlorine that can corrode an overlying aluminuminterconnect and adversely affect the device.

A first embodiment of a method of the present invention is describedwith reference to FIGS. 1A-1D, in a method of forming a conductivecontact 34. In the illustrated example, the contact 34 comprisestitanium nitride or boron-doped titanium nitride. The contact isillustrated and will be described as being coupled to a diffusionregion. However, the contacts of the present invention can be usedwherever required within the structure of a semiconductor circuit.

Referring to FIG. 1A, a semiconductive wafer fragment 10 is shown at apreliminary processing step. The wafer fragment 10 in progress cancomprise a semiconductor wafer substrate or the wafer along with variousprocess layers formed thereon, including one or more semiconductorlayers or other formations, and active or operable portions ofsemiconductor devices.

The wafer fragment 10 is shown as including a silicon-comprising baselayer or substrate 12. An exemplary substrate 12 is monocrystallinesilicon that is typically lightly doped with a conductivity enhancingmaterial. Formed at the surface 14 of the substrate 12 are a transistorstructure 16 and an overlying insulative layer 18. The transistor 16,comprising a gate 20 and adjacent source/drain diffusion regions 22 a,22 b, can be formed by conventional methods known and used in the art.

The insulative layer 18 comprises an oxide, for example, silicon dioxide(SiO₂), phosphosilicate glass (PSG), borosilicate glass (BSG), andborophosphosilicate glass (BPSG), in a single layer or multiple layers,being BPSG in the illustrated embodiment. The BPSG insulative layer 18has been etched using a known photolithography technique, for example,reactive ion etching (RIE), while masking with a patterned photoresistlayer (not shown) to provide a via or other contact opening 24 definedby insulative sidewalls 26 and a bottom portion 28. The contact openingextends to the diffusion region 22 a (i.e., source/drain region) in theunderlying silicon substrate 12 to which electrical contact is to bemade.

Referring to FIG. 1B, a titanium silicide (TiSi_(x)) seed layer 30 isformed over the exposed surfaces 14, 18 respectively, of the siliconsubstrate at the bottom 28 of the contact opening 24 and the insulativelayer 18. Typically, the seed layer is formed to a thickness of about250 to about 300 angstroms. The resulting TiSi_(x) seed layer 30 thatforms at the interface with the diffusion region 22 a is useful to lowerresistance in the contact region. Techniques and process systems forforming a titanium silicide layer are well known in the art, asdescribed, for example, in U.S. Pat. No. 6,086,442 (Sandhu, et al.) andU.S. Pat. No. 5,976,976 (Doan, et al.), the disclosures of which areincorporated by reference herein.

Preferably, the TiSi_(x) seed layer 30 is formed by a conventionalplasma enhanced chemical vapor deposition (PECVD) process that comprisesforming an RF plasma from source gases comprising titanium tetrachloride(TiCl₄), hydrogen (H₂), a silicon precursor such as silane (SiH₄) ordichlorosilane (SiH₂Cl₂), and carrier gases such as argon (Ar) and/orhelium (He) to deposit a layer of titanium silicide (TiSi_(x)) over thesubstrate (silicon) surface 14 and the surface 19 of the insulativelayer 18. Exemplary process conditions for achieving the formation ofthe TiSi_(x) seed layer 30 include a temperature of about 650° C., aprocess pressure of about 0.5 to about 20 Torr, an rf power range ofabout 400 watts, and flow rates of about 150 to about 300 sccm TiCl₄,about 1000 to about 8000 sccm hydrogen (H₂), about 1 to about 100 sccmsilane (SiH₄), about 1000 sccm argon (Ar), and about 50 sccm nitrogen(N₂).

Although the preferred process for forming the TiSi_(x) seed layer is byPECVD technique, the TiSi_(x) seed layer 30 can also be formed by adepositing a thin layer of titanium by physical vapor deposition (PVD),i.e., sputtering, onto the surface 14 of the substrate 12 at the bottomof the contact opening, and then performing an anneal step (about 650°C.) in an ambient gas such as nitrogen, argon, ammonia, or hydrogen.This causes the titanium to react with the silicon exposed on thesurface 14 of the diffusion region 22 a to form the TiSi_(x) seed layer30. Such a process is said to be self-aligning, as the TiSi_(x) is onlyformed where the titanium metal contacts the silicon active regions.

Another example of a method to deposit the TiSi_(x) seed layer 30 is bya conventional low pressure CVD (LPCVD) process. Exemplary processconditions include a process temperature of about 650° C. to about 900°C., and a pressure of about 10 mTorr to about 1 Torr, using titaniumtetrachloride (TiCl₄) plus a silicon precursor or source gas such assilane (SiH₄) or dichlorosilane (SiH₂Cl₂) at a ratio of about 5:1, in acarrier gas such as helium.

To overcome the problems that occur in the use of a pure TiCl₄-basedtitanium nitride plug or contact, such as peeling of the contact fromthe insulative sidewalls of the contact opening and cracking of theinsulative layer, the invention utilizes a boron-doped, TiCl₄-basedtitanium nitride fill (titanium boronitride) to form the conductivecontact or plug. Preferably, the foregoing conductive contact is formedby a conventional thermal chemical vapor deposition (TCVD) process. SuchTCVD techniques and process systems are well known in the art, asdescribed, for example, in U.S. Pat. No. 6,037,252 (Hillman et al.), andU.S. Pat. No. 5,908,947 (Iyer and Sharan), the disclosures of which areincorporated by reference herein. TCVD systems include standard thermalreactors such as cold wall/hot substrate reactors and hot wall reactors,plasma-assisted reactors, radiation beam assisted reactors, and thelike.

Typically, in a TCVD process, the substrate is placed in a reactionchamber (not shown) in which the substrate and/or the gaseous precursoris heated. Preferably, the substrate is heated to a temperature inexcess of the decomposition temperature of the precursor gases. When thegases are introduced into the reaction chamber and brought into contactwith the substrate, the gases decompose on the surface of the substrateto deposit the titanium boronitride film comprising the metal andelements of the precursor or reactant gases.

In an exemplary TCVD process to deposit a titanium nitride (TiN) orboron-doped TiN (TiB_(x)N_(y)) layer according to the invention usinghot or cold wall thermal chemical vapor deposition, the wafer fragment10 is positioned in the TCVD reactor (not shown) and a source gascomprising titanium tetrachloride (TiCl₄), ammonia (NH₃), one or moreinert carrier gases such as argon, helium and/or nitrogen, and diborane(B₂H₆) to form a boron-doped TiN layer, is flowed into the reactor underconditions effective to chemical vapor deposit a layer 32 of TiCl₄-basedtitanium (doped or undoped) nitride over the titanium silicide(TiSi_(x)) seed layer 30 within the contact opening 24. The gaseousmaterial is blanket deposited to a thickness to completely fill thecontact opening, resulting in the structure shown in FIG. 1C. Preferredflow rates of the precursors are about 100 to about 500 sccm TiCl₄,about 100 to about 1000 sccm NH₃, and about 100 to about 1000 sccm B₂H₆(for a boron-doped film). The preferred temperature within the reactor(hot wall) or of the susceptor (cold wall) is from about temperature ofabout 550 to about 700° C., preferably about 560 to about 650° C., withpressure conditions within the reactor being from about 1 Torr to about15 Torr, preferably about 10 Torr. Typically, to fill a contact opening,about 1000 to about 3000 angstroms of material is typically deposited.

High-aspect-ratio contacts (aspect ratio of 3:1 or greater) that aremade of TiCl₄-based TiN without the inclusion of B₂H₆ in the source gas,and have a thickness greater than about 150 to about 200 angstroms,possess a reduced level of adherence to the insulative sidewalls of acontact opening. This results in the contact peeling away from thesidewalls of the opening. In addition, when such contacts reach athickness of about 200 angstroms or more, the high thermal stress of thefill material can cause cracking of the insulative layer. With theaddition of increasing amounts of B₂H₆ to the TiCl₄ and NH₃ gaseouscomponents, there is an increase in the adhesion of the fill material ofthe contact 34 with the insulative sidewalls 26 of the opening 24, and areduction in the thermal stress level, which substantially eliminatescracking of the insulative layer 18. However, as the amount of boronincreases, there is also a reduction in the level of conductivity (andincrease in resistance) of the contact 34. To counteract this effect,the ammonia in the gas mixture is provided in an amount effective tomaintain the conductivity of the formed contact 34 at a predeterminedlevel for an effective electrical contact with the diffusion area 22 aor other semiconductor structure.

The inclusion of B₂H₆ in the source gas results in a TiCl₄-based, borondoped titanium nitride conductive layer 32 having the general formulaTiB_(x)N_(y) (titanium boronitride). Such films are particularly usefulas a fill in high-aspect-ratio contact openings and vias, particularlythose having an aspect ratio of 3:1 or greater. The amounts of the B₂H₆and the NH₃ gases that are flowed into the system are maintained so asto provide a fill having a level of adherence to the insulativesidewalls 26 of the contact opening 24 such that the formed contact 34remains attached to and does not peel away from the sidewalls, and nosubstantial cracks develop in the body of the insulative layer 18.

After deposition of the titanium nitride (doped or undoped) fillmaterial, excess material 32 is removed from the surface 19 of theinsulative layer, leaving the fill in the opening 24 to form theconductive contact or plug 34, as shown in FIG. 1D. The contact 34provides electrical connection to/from the diffusion region (conductivearea) 22 a to various parts of the semiconductor device. The excessmaterial 32 can then be removed according to a conventional method knownin the art, preferably, by chemical mechanical polishing (CMP).

The contact 34 is then subjected to a heat treatment, preferably with arapid thermal anneal process, to at least about 700° C., preferablyabout 700 to about 800° C., in a nitrogen-containing gas, preferablyammonia (NH₃), for a time of up to about 20 seconds, to drive outchlorine (Cl₂) incorporated into the contact from the TiCL₄ precursorduring deposition. Preferably, the heat treatment reduces theconcentration of chlorine in the contact by at least about 50% by wt.,preferably by at least about 75% by wt., more preferably by at leastabout 95% by wt.

Advantageously, the present process of first removing the excess contactmaterial by CMP, and then thermally annealing the titanium nitride fillmaterial remaining as the contact 34 in a nitrogen-containing gas suchas ammonia, reduces the chlorine content in the fill material withoutsignificantly changing the other properties of the film stack,particularly the advantages provided by the incorporation of boron intothe film layer.

The resulting contact 34 comprises a titanium nitride layer (boron-dopedor undoped) overlying a titanium silicide layer deposited onto thesubstrate at the bottom of the contact opening. The contact 34 possessesa reduced level of chlorine (Cl₂) as a result of the thermal anneal inammonia (NH₃) or other nitrogen-containing gas. Preferably, the chlorinecontent of the contact following the anneal is less than about 4% bywt., preferably less than 3% by wt., more preferably less than about 1%by wt. Boron-doped titanium nitride contacts also possess a high levelof adhesion to the insulative sidewalls of the opening, have asufficiently low thermal stress level, measured in force per unit area(i.e., Gdynes/cm²), to substantially eliminate cracking of theinsulative layer, and are highly conductive with low electricalresistivity.

Although not shown, a passivation layer can then be formed over thedevice. Optionally, other interconnects and contact structures (notshown) can be formed overlying the present structure.

In another embodiment of the method of the invention, a multi-layeredboron-doped and undoped titanium nitride contact can be fabricated in awafer fragment, as depicted in FIGS. 2A-2F.

Referring to FIG. 2A, a wafer fragment 10′ is shown before processing.Briefly, wafer fragment 10′ includes a silicon-comprising substrate 12′,for example, monocrystalline silicon, with an active area 22 a′ such asa source/drain region. An overlying insulative layer 18′ comprising, forexample, BPSG, has an exposed surface 19′ and a contact opening 24′having sidewalls 26′ and a bottom portion 28′. The contact opening 24′extends to the active area 22 a′.

Referring to FIG. 2B, a thin titanium silicide (TiSi_(x)) layer 30′ isformed over the active area 22 a′ at the bottom 28′ of the opening 24′.The TiSi_(x) layer 30′ preferably has a thickness of about 250 to about300 angstroms. The TiSi_(x) layer 30′ can be formed by conventionalmethods, as previously described, and preferably by PECVD using TiCl₄,H₂, and one or more carrier gases.

A layered contact is formed by depositing alternating layers ofTiCl₄-based titanium nitride and a boron-doped TiCl₄-based titaniumnitride into the contact opening, such that a boron-doped titaniumnitride layer is interposed between two layers of non-doped titaniumnitride. The multi-layered contact can be formed by conventional thermalCVD processing at a temperature of about 550 to about 700° C.,preferably about 560 to about 650° C., and a pressure of about 1 Torr toabout 15 Torr, preferably about 10 Torr.

A gas mixture comprising titanium tetrachloride (TiCl₄) and ammonia(NH₃) and one or more carrier gases can be flowed into the reactor toform a layer 36 a′ of non-doped titanium nitride onto the TiSi_(x) seedlayer 30′ to a desired thickness, typically about 100 to about 500angstroms, resulting in the structure shown in FIG. 2C. Preferred flowrates for the gas mixture are about 100 to about 500 sccm TiCl₄ andabout 100 to about 1000 sccm NH₃.

As shown in FIG. 2D, diborane (B₂H₆) is then flowed into the reactor,and a layer 32′ comprising boron-doped, titanium nitride is depositedonto the non-doped titanium nitride layer from a gas mixture comprisingTiCl₄, NH₃, and B₂H₆. The boron-doped, titanium nitride layer 32′ isdeposited to a desired thickness of about 100 to about 500 angstroms.Preferred flow rates for the gas mixture are about 100 to about 500 sccmTiCl₄, about 100 to about 1000 sccm NH₃, and about 100 to about 1000sccm B₂H₆. As previously discussed, the flow of NH₃ and B₂H₆ can becontrolled to modify the adhesiveness, thermal stress level, andconductivity of the resulting multi-layered contact.

The flow of B₂H₆ is then ceased, and the first source gas mixture (i.e.,TiCl₄, NH₃) is flowed into the reactor to form a layer 36 b′ comprisingundoped titanium nitride, as shown in FIG. 2E. The titanium nitridelayer 36 b′ is deposited to a desired thickness, typically about 100 toabout 500 angstroms. The titanium nitride layer 36 b′ can be depositedto fill the opening. Alternatively, additional layers of boron-dopedtitanium nitride can be deposited between two layers of non-dopedtitanium nitride as desired to fill the contact opening 24′, with theuppermost layer of the contact comprising non-doped titanium nitride.

Excess fill material is then removed as depicted in FIG. 2F, forexample, by CMP, to form the conductive contact 34′.

The contact 34′ is then subjected to a thermal anneal at an elevatedtemperature, preferably greater than 700° C., preferably about 700° C.to about 800° C., in a nitrogen-containing atmosphere, preferablyammonia (NH₃), to drive the chlorine (Cl₂) deposited from the TiCl₄precursor out of the contact material.

Sandwiching a layer of boron-doped titanium nitride 32′ between undopedtitanium nitride substantially reduces the thermal stress in aTiCl₄-based TiN fill material. This allows the fill to be used as aconductive contact to replace tungsten (W) plugs in high aspect ratiofeatures. The combination of alternating layers achieves a TiCl₄-basedTiN contact having a level of adhesion that substantially eliminatespeeling of the formed contact from the sidewalls of the contact opening.It also provides a lowered level of thermal stress that substantiallyreduces cracking of the body of the insulative layer, particularly whenthe thickness of the contact reaches about 500 angstroms or greater. Inaddition, the resulting contact has a high level of conductivity for aneffective electrical contact to a diffusion region or other conductivestructure. The removal or reduction of chlorine (or other component)from the contact material by a high temperature anneal in ammonia (orother reactive gas) provides a contact having increased compatibilitywith an adjacent or overlying conductive material, for example, analuminum interconnect. In addition, conducting the thermal anneal stepafter removing excess conductive material from the surface of thesubstrate eliminates problems encountered with cracking of the filmlayer and/or the substrate with thermal anneals performed on a blanketmaterial layer overlying the substrate.

EXAMPLE 1

A boron-doped TiCl₄-based titanium nitride (TiN) contact was formed in ahigh aspect ratio opening of a BPSG layer, without removal of chlorineby RTP anneal. The flow of diborane (B₂H₆) was varied over a range totest the change in thermal stress (Gdynes/cm²) of the boron-doped,TiCl₄-based TiN contact on the BPSG insulative layer.

A wafer fragment was provided that had a silicon substrate layer and anoverlying layer of BPSG. A contact opening was formed through the BPSGlayer. The aspect ratio of the opening was 10:1.

The TiCl₄-based TiN film was deposited by thermal CVD at a pressure of10 Torr using a Centura system, available from Applied Materials companyof Santa Clara, Calif. The precursor gases were flowed into the reactoras follows: 340 sccm TiCl₄, 200 sccm NH₃, 3000 sccm argon (Ar), and 2000sccm gaseous nitrogen (N₂). The diborane (B₂H₆) was flowed into thereactor at a rate ranging from 200 sccm to 600 sccm. Data was measuredat two different temperatures: 600° C. and 650° C.

The results are shown in a graphical form in FIGS. 3A and 3B. Asindicated, as the amount of boron (i.e., B₂H₆) was increased, the stress(Gdynes/cm²) of the TiCl₄-based TiN material decreased to a neutral orzero stress level and below. Thus, by varying the B₂H₆ flow, the thermalstress of the TiCl₄-based TiN film can be adjusted such that thematerial does not cause the insulative layer (e.g., BPSG) to crack.

EXAMPLE 2

A boron-doped TiCl₄-based titanium nitride (TiN) contact was formed in ahigh aspect ratio opening of a BPSG layer according to the method of theinvention. A boron-doped TiN film was formed in a contact opening (10:1aspect ratio) in a BPSG layer overlying a silicon substrate, asdescribed in Example 1.

Excess titanium nitride film material was removed from the surface ofthe BPSG layer by conventional CMP, leaving the film material within thecontact opening. The wafer was then subjected to a high temperatureanneal by rapid thermal processing (RTP) in an ammonia (NH₃) atmosphereat 750° C. for 25 seconds. PEELS micrographs showed differences in thechlorine (Cl₂) content of the boron-doped titanium nitride materialbefore and after the high temperature anneal.

In compliance with the statute, the invention has been described inlanguage more or less specific as to structural and methodical features.It is to be understood, however, that the invention is not limited tothe specific features shown and described, since the means hereindisclosed comprise preferred forms of putting the invention into effect.The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

1. A method of forming a material layer on a substrate, comprising the steps of: forming the material layer on the substrate to a thickness of about 500 angstroms or greater, the material layer comprising a component capable of diffusing into and corroding an adjacent metal layer; and heat treating the material layer using a reactive gas at a temperature of about 550° C. or greater to remove an effective amount of the component from the material layer to eliminate corrosion of said adjacent metal layer without forming substantial cracks within the material layer.
 2. A method of forming a material layer on a substrate, comprising the steps of: forming a metal nitride layer on the substrate to a thickness of about 500 angstroms or greater, the metal nitride layer comprising a component capable of diffusing into and corroding an adjacent metal layer; and heat treating the metal nitride layer using a reactive gas at a temperature of about 550° C. or greater to remove an effective amount of the component from the metal nitride layer to eliminate corrosion of said adjacent metal layer by said component, without forming substantial cracks within the metal nitride layer.
 3. A method of forming a conductive material layer on a substrate, comprising the steps of: forming a layer of titanium nitride on the substrate to a thickness of about 500 angstroms or greater, the titanium nitride layer comprising chlorine; and heat treating the titanium nitride layer using a reactive gas at a temperature of about 550° C. or greater to remove an effective amount of the chlorine from the titanium nitride layer to eliminate corrosion of an adjacent metal layer by said chlorine.
 4. A method of forming a conductive material layer on a substrate, comprising the steps of: forming a layer of titanium boronitride on the substrate to a thickness of about 500 angstroms or greater, the titanium boronitride layer comprising chlorine; heat treating the titanium boronitride layer using a reactive gas at a temperature of about 550° C. or greater to remove an effective amount of the chlorine from the titanium boronitride layer to eliminate corrosion of an adjacent metal layer by said chlorine.
 5. A method of forming a conductive material layer on a substrate, comprising the steps of: forming a layer of titanium nitride on the substrate to a thickness of about 500 angstroms or greater, the titanium nitride layer comprising chlorine; forming a layer of titanium boronitride on the titanium nitride layer to a thickness of about 500 angstroms or greater, the titanium boronitride layer comprising chlorine; repeating the steps of forming the titanium nitride layer and the titanium boronitride layer to form the material layer to a thickness of about 500 angstroms or greater, the material layer comprising sequential layers of titanium nitride and titanium boronitride; and heat treating the material layer in a reactive gas at a temperature of about 550° C. or greater to remove an effective amount of the chlorine from the material layer to reduce corrosion of an adjacent metal layer by said chlorine.
 6. A method of forming a conductive material layer on a substrate, comprising the steps of: depositing a gas comprising titanium tetrachloride and ammonia onto a substrate to form a layer of titanium nitride to a thickness of about 500 angstroms or greater, the titanium nitride layer comprising chlorine; and heat treating the titanium nitride layer using a reactive gas at a temperature of about 550° C. or greater to remove an effective amount of the chlorine from the titanium nitride layer to reduce corrosion of an adjacent metal layer by said chlorine.
 7. A method of forming a conductive material layer on a substrate, comprising the steps of: depositing a gas comprising titanium tetrachloride, ammonia, and diborane onto a substrate to form a layer of titanium boronitride to a thickness of about 500 angstroms or greater, the titanium boronitride layer comprising chlorine; and heat treating the titanium boronitride layer in a reactive gas at a temperature of about 550° C. or greater to remove an effective amount of the chlorine from the titanium boronitride layer to reduce corrosion of an adjacent metal layer by said chlorine.
 8. A method of forming a conductive material layer on a substrate, comprising the steps of: depositing a first gas comprising titanium tetrachloride and ammonia onto a substrate to form a layer of titanium nitride to a thickness of about 100-500 angstroms, the titanium nitride layer comprising chlorine; depositing a second gas comprising titanium tetrachloride, ammonia, and diborane onto the titanium nitride layer to form a layer of titanium boronitride to a thickness of about 100-500 angstroms, the titanium boronitride layer comprising chlorine; repeating the steps of depositing the first and second gases to form the material layer to a thickness of about 500 angstroms or greater, the material layer comprising sequential layers of titanium nitride and titanium boronitride; and heat treating the material layer in a reactive gas at a temperature of about 550° C. or greater to remove an effective amount of the chlorine from the material layer to reduce corrosion of an adjacent metal layer by said chlorine.
 9. A method of forming a material layer on a substrate, comprising the steps of: forming a metal nitride layer on the substrate to a thickness of about 500 angstroms or greater, the metal nitride layer comprising a component capable of diffusing into and corroding an adjacent metal layer; and heat treating the metal nitride layer using a reactive gas at a temperature of about 700° C. or greater to remove an effective amount of the component from the metal nitride layer to eliminate corrosion of said adjacent metal layer by said component, without forming substantial cracks within the metal nitride layer.
 10. A method of forming a fill, comprising the steps of: forming a fill of about 500 angstroms or greater within an opening in a substrate, the fill comprising a component capable of diffusing into and corroding an adjacent metal layer; and heat treating the fill using a reactive gas at a temperature of about 550° C. or greater to remove an effective amount of the component from the fill to eliminate corrosion of said adjacent metal layer by said component, without forming substantial cracks within the fill.
 11. The method of claim 10, wherein the opening has an aspect ratio of at least about 3:1.
 12. A method of forming a fill, comprising the steps of: forming a fill of about 500 angstroms or greater within an opening in a substrate, the fill comprising metal nitride and a component capable of diffusing into and corroding an adjacent metal layer; and heat treating the fill using a reactive gas at a temperature of about 550° C. or greater to remove an effective amount of the component from the fill to eliminate corrosion of said adjacent metal layer by said component.
 13. The method of claim 12, wherein the component comprises chlorine.
 14. A method of forming a fill, comprising the steps of: forming a fill of about 500 angstroms or greater within an opening in a substrate, the fill comprising titanium nitride and chlorine; and heat treating the fill using a reactive gas at a temperature of about 550° C. or greater to remove an effective amount of the chlorine from the fill to eliminate corrosion of an adjacent metal layer by said chlorine.
 15. A method of forming a fill, comprising the steps of: forming a fill of about 500 angstroms or greater within an opening in a substrate, the fill comprising titanium boronitride and chlorine; and heat treating the fill using a reactive gas at a temperature of about 550° C. or greater to remove an effective amount of the chlorine from the fill to eliminate corrosion of an adjacent metal layer by said chlorine.
 16. A method of forming a fill, comprising the steps of: forming a layer of titanium nitride within an opening in a substrate to a thickness of about 500 angstroms or greater, the titanium nitride layer comprising chlorine; forming a layer of titanium boronitride on the titanium nitride layer to a thickness of about 500 angstroms or greater, the titanium boronitride layer comprising chlorine; repeating the steps of forming the titanium nitride layer and the titanium boronitride layer to form the fill to a thickness of about 500 angstroms or greater, the fill comprising sequential layers of titanium nitride and titanium boronitride; and heat treating the fill in a reactive gas at a temperature of about 550° C. or greater to remove an effective amount of the chlorine from the fill to reduce corrosion of an adjacent metal layer by said chlorine.
 17. A method of forming a fill, comprising the steps of: depositing a gas comprising titanium tetrachloride and ammonia onto a substrate within an opening to form a fill comprising titanium nitride and chlorine, the fill having a thickness of about 500 angstroms or greater; and heat treating the fill in a reactive gas at a temperature of about 550° C. or greater to remove an effective amount of the chlorine from the fill to reduce corrosion of an adjacent metal layer by said chlorine.
 18. A method of forming a fill, comprising the steps of: depositing a gas comprising titanium tetrachloride, ammonia, and diborane onto a substrate within an opening to form a fill comprising titanium boronitride and chlorine, the fill having a thickness of about 500 angstroms or greater; and heat treating the fill in a reactive gas at a temperature of about 550° C. or greater to remove an effective amount of the chlorine from the fill to reduce corrosion of an adjacent metal layer by said chlorine.
 19. A method of forming a fill, comprising the steps of: depositing a first gas comprising titanium tetrachloride and ammonia onto a substrate within an opening to form a first layer comprising titanium nitride and chlorine, the first layer having a thickness of about 100-500 angstroms; depositing a second gas comprising titanium tetrachloride, ammonia, and diborane into the opening to form a second layer comprising titanium boronitride and chlorine, the second layer having a thickness of about 500 angstroms or greater; and repeating the steps of depositing the first and second gases to form the fill to a thickness of about 500 angstroms or greater, the fill comprising sequential layers of titanium nitride and titanium boronitride; and heat treating the fill in a reactive gas at a temperature of about 550° C. or greater to remove an effective amount of the chlorine from the fill to reduce corrosion of an adjacent metal layer by said chlorine.
 20. A conductive contact, comprising a metal nitride fill within an opening in a substrate, the fill having a thickness of about 500 angstroms or greater, and formed using a gas comprising a metal chloride gas and a nitrogen-based gas, and heat treated at a temperature of about 550° C. or greater to remove an effective amount of the chlorine from the fill to reduce corrosion of an adjacent metal layer by said chlorine.
 21. A conductive contact, comprising a titanium nitride fill within an opening in a substrate, the fill having a thickness of about 500 angstroms or greater, and formed using a gas comprising titanium tetrachloride and a nitrogen-based gas, and heat treated at a temperature of about 550° C. or greater to remove an effective amount of chlorine from the fill to reduce corrosion of an adjacent metal layer by said chlorine.
 22. A conductive contact, comprising a titanium boronitride fill within an opening in a substrate, the fill having a thickness of about 500 angstroms or greater, and formed using a gas comprising titanium tetrachloride, a nitrogen-based gas, and diborane, and heat treated at a temperature of about 550° C. or greater to remove an effective amount of chlorine from the fill to reduce corrosion of an adjacent metal layer by said chlorine.
 23. A conductive contact, comprising a metal nitride fill within an opening in a substrate, the fill comprising alternating layers of titanium nitride and titanium boronitride, and a thickness of about 500 angstroms or greater, the fill formed using a first gas comprising titanium tetrachloride and a nitrogen-based gas and a second gas comprising titanium tetrachloride, a nitrogen-based gas and diborane, and heat treated at a temperature of about 550° C. or greater to remove an effective amount of chlorine from the fill to reduce corrosion of an adjacent metal layer by said chlorine.
 24. A semiconductor device, comprising a conductive contact according to claim
 20. 25. A memory device, comprising: an array of memory cells; internal circuitry; and a conductive contact according to claim 20, coupled to the memory array and the internal circuitry.
 26. An integrated circuit supported by a substrate, and comprising a conductive contact according to claim
 20. 27. A semiconductor device, comprising a metal nitride layer on a substrate, the metal nitride layer having a thickness of about 500 angstroms or greater, and formed using a gas comprising a metal chloride gas and a nitrogen-based gas, and heat treated at a temperature of about 550° C. or greater to remove an effective amount of the chlorine from the metal nitride layer to reduce corrosion of an adjacent metal layer by said chlorine.
 28. The device of claim 27, wherein the metal nitride layer comprises titanium nitride.
 29. The device of claim 27, wherein the metal nitride layer comprises titanium boronitride.
 30. The device of claim 27, wherein the metal nitride layer comprises alternating layers of titanium nitride and titanium boronitride, each layer about 100-500 angstroms thick. 